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Introduction

Raspberry Pi Thermometer

A Raspberry Pi 3 with all cores running at 100% gets very hot, an example is when SETI is running. With a good heatsink
such as a FLIRC case the core temperature is kept about 15-20 degrees Centigrade above ambient. This is fine until the ambient temperature
starts rising beyond 30 Degrees Centigrade which happened during a recent heatwave.

I looked at using some PC heatsink style 5V fans powered by the raspberry Pi psu but they were noisy and on all the time - very distracting!
It crossed my mind to use a Pi Zero and a temperature sensor to switch the fans on and off when my room temperature raised above 25
Degress C. A little research led me to the
ModMyPi website
which shows a simple example using a DS18B20 sensor. I used this as my starting point.
I built a prototype on breadboard and started to write the code to do the switching. This quickly expanded to include a simple bargraph
display for room temperature, a flashing LED for confidence that the Pi is running, logs on/off events and a shutdown button.

I bought a couple of cheap desktop USB fans which turned out to be considerably quieter and more efficient than the PC versions.
My 13 SETI Pi's/Odroids are now kept nice and cool - and only when needed....